This invention relates to a water seal device for a rotary shaft in a hydraulic machine, such as a water seal device for a rotary shaft suitable for use in a large-sized hydraulic machine, for example, a turbine for a hydraulic power plant, and more particularly to a shaft seal to seal water on the outer peripheral surface of a rotary shaft by solid packing.
FIG. 1 shows the hydraulic power plant in common use. The power plant of this type comprises: a runner 1 to convert a potential energy of water into a kinetic energy; a generator to convert the kinetic energy of the runner into an electric energy; a main shaft 3 connecting the runner to the generator; a casing 4 to uniformly introduce water, which has passed through a hydraulic steel piping from an upper reservoir, to the entire periphery of the runner; guide vanes 5 to adjust a flow rate of the water thus introduced; an upper and lower covers 6 and 7 to cover the top and bottom of the runner; a draft pipe 8 and a tube 9 for leading the water, which has left the runner to a lower reservoir. In the power plant of the type described, in order to prevent water under pressure in a housing chamber of the runner to be blown out along the outer periphery of the main shaft 3, there is provided a rotary shaft water seal device 10 around the main shaft 3 in the upper cover 6.
FIGS. 2 through 5 show the conventional rotary shaft water seal device of the type described. This device includes two carbon packings 12, 13 and a resin packing 14, each of which consists of a plurality of circular arcuate segments (all of which are solid packings), and these solid packings are received in an arrangement of three stages in an annular packing box solidly secures to the upper cover 6 at the outer periphery of a liner 3A of the main shaft 3. The packing box 11 is provided therein with support surface portions 11A, 11B and 11C which are disposed in three stages in the vertical direction, respectively. The resin packing 14 is mounted on the lower support surface portion 11A, one of the carbon packings 13 on the middle stage support surface portion 11B, and the other of the carbon packings 12 on the upper support surface portion 11C, respectively. The upper surface of the carbon packing 12 is blocked by a cover portion 11D of the packing box 11.
The inner peripheral surfaces of the solid packings 12, 13 and 14 are in sliding contact with the outer peripheral surfaces of the liner 3A of the main shaft 3 and pressed against the liner 3A of the main shaft 3 by a spring 15 wound around the outer periphery of the respective packings.
Description will now be given of the arrangement of the solid packing in conjunction with an example of the carbon packing 12 mounted on the upper stage. This packing is of such an arrangement in which a plurality of circular arcuate segments 12A are annularly arranged with a slight gap G being held between the adjacent segments. The segments 12A is each provided in a guide groove 17 formed at an intermediate portion between the adjacent segments 12A with a guide member 16 to guide the segment to be displaced in the radial direction of the rotary shaft and prevent the segment to be displaced in the circumferential direction. Each of the guide members 16 is solidly secured to the support surface 11C of the packing box by means of a set-screw.
Description will now be given of the reasons for adopting such a construction that the aforesaid gap G is taken and the segments are permitted to be displaced in the circumferential direction. The inner peripheral surfaces of the segments 12A are worn due to sliding contact with the liner 3A of the main shaft 3. Assumption is made that the segments are solidly secured to one another in an annular state with the adjacent segments being abutted against each other. Due to the wear on the inner peripheral surfaces the segments, a gap is generated between the inner peripheral surface of the packing and the outer peripheral surface of the liner and progressively developed. In order to prevent the development of this gap, the packing should be decreased in diameter, following the extent of wear. The above-described arrangement has been adopted to secure this decrease in diameter of the packing.